Compounds containing 1-oxa-3-aza-tetraline groups, and their prepolymers, are known, for example, from Swiss Pat. Nos. 574,978, 579,113 and 606,169. They can be obtained, for example, from phenols by reaction with formaldehyde and an amine, according to the formula: ##STR1## wherein R is, for example, hydrogen, halogen, alkyl or alkoxy, and R' is an aliphatic or aromatic group. In contrary to other known condensation reactions of phenols, amines and formaldehyde, in the reaction outlined above phenolic OH-groups are consumed. It is thereby possible, according to the formula (a) hereinabove, to determine the amount of the synthesized 1-oxa-3-aza tetraline group from the analytic determination of the said OH-groups in the rection mixture.
It is also known from the above-mentioned patents that these compounds containing 1-oxa-3-aza-tetraline groups can be cured with epoxide resins, including cycloaliphatic epoxide resins. The products obtained up to now have been useful for various applications, but their stability is limited. The Martens heat stability of the hardest resins obtained up to now is only between about 120.degree. C. and 135.degree. C., with peak values from about 160.degree. C. to 170.degree. C.
For many applications, higher heat stabilities are necessary. For example, electric insulating materials of high heat stability are a constant requirement of the electric industry. Plastics reinforced with glass, quartz, carbon fibers and the like would probably be considered for many new areas of application if the heat resistance of the polymeric resin could be increased.